Facteurs favorisant l'enfoncement du séquestre après ostéotomie transtrochantérique de rotation antérieure pour ostéonécrose de la tête fémorale

Background Transtrochanteric anterior rotational osteotomy (ARO) for osteonecrosis of the femoral head (ONFH) can preserve for a long-time collapsed femoral head. Progressive collapse of anteriorly-transposed necrotic lesion leads to secondary arthritic changes and clinical failure. Critical factors influencing collapse of the transposed necrotic lesion after ARO remain largely unknown. Therefore, we performed a retrospective study of ARO to determine: 1) if pre-operative collapse influences collapse of the transposed necrotic area, 2) if any other factor may influence collapse of the transposed necrotic area. Hypothesis We hypothesized the degree of pre-operative femoral head collapse influences progressive collapse of the transposed necrotic lesion after ARO. Materials and methods We reviewed 47 hips in 42 patients with ONFH treated with ARO between 2000 and 2005 with a mean follow-up of 11.4 years (10–14 years). The occurrence of progressive collapse of the transposed necrotic lesion after ARO was examined using lateral radiographs taken at least once every year after ARO. The following factors were statistically analyzed: age, sex, body mass index, Harris Hip Score (HHS), pre-operative level of collapse, extent of the necrotic lesion and post-operative intact ratio (ratio of the transposed intact articular surface of the femoral head). Results Progressive collapse of the transposed necrotic lesion (progressive collapse group) was seen in 17 hips (36 %) during a mean period of 1.8 years (0.5–3.7 years) after ARO, which has developed within 4 years in all cases. Pre-operative level of collapse in the progressive collapse group (4.4 ± 1.4 mm) was significantly larger than that in the non-progressive collapse group (2.1 ± 1.0 mm), which was independently associated with progressive collapse of the transposed necrotic lesion in multivariate analysis (P < 0.0001) with cutoff point of 2.98 mm. In univariate analysis, lower pre-operative HHS, severe extent of the necrotic lesion and the lower post-operative intact ratio were also associated with progressive collapse of the transposed necrotic lesion, but were not associated as independent factors in multivariate analysis. Discussion The current study suggests that progressive collapse of the transposed necrotic lesion after ARO depends mainly on the pre-operative level of collapse (cutoff point = 2.98 mm). Level of evidence IV; retrospective case series.